Almost a year since the tragic events in the Indian Ocean,
we look back at the tragic events of 26 December 2004 – and
ask: could it happen again?

by Stuart Carter

This
is the story of a force of Nature so powerful that it killed over
300,000 people, most of them in Sumatra. The destruction it caused
has been likened to a nuclear attack. What made it so powerful?
And could it happen again?

It’s now
almost a year since the tsunami struck and the world is still struggling
to come to terms with the enormity of the disaster.

The story starts
in the early morning of 26 December 2004. In Sumatra, fishermen
are already on the water. In Sri Lanka, 1500 people begin their
train journey from Colombo to Galle. In Thailand, beach-front restaurants
are opening up. And in Hawaii, scientists at the Pacific Tsunami
Warning Center are testing their systems. All these people are totally
unaware that they are about to be caught up in one of the worst
ever natural catastrophes.

Shortly after
dawn and entirely without warning, a huge earthquake rips across
the ocean floor south of Sumatra.

Traditional
Japanese view of a tsunami

It happens at
the junction of two of the great rafts of rock – tectonic
plates – that make up the Earth’s crust. Driven by convecting
heat from within the planet, these plates are always on the move.
And where they collide, massive forces are unleashed.

Under the ocean
off Sumatra, the Indo-Australian plate is grinding underneath the
Eurasian plate, in a process called subduction. It’s been
going on for 20 million years. On 26 December last year, something
snapped.

Phil
Cummins of Geoscience Australia has been studying earthquakes in
the region for over 15 years. He fills in the details: “As
the Indo-Australian plate is subducted beneath Indonesia, it pulls
it down and deforms the upper plate. The process builds up strain
energy. Eventually the stress on that contact exceeds the strength
of the contact, and the upper plate snaps back into position”.

The earthquake’s
epicentre is 155 miles to the southwest of Aceh province which lies
in the northern part of Sumatra. The provincial capital, Banda Aceh,
feels the full force of the earthquake; and buildings collapse.
The town is wrecked 20 minutes before the tsunami arrives.

Minutes after
the earthquake rips through the Earth’s crust, its waves are
recorded by a seismometer over 8000 miles away in California. The
seismogram shows that the earthquake continued for over four minutes.
Later analysis will confirm that it measures 9.0 on the Richter
scale, making it one of the most violent on record. It’s more
powerful than all the world’s earthquakes over the previous
five years put together.

Halfway across
the world in Hawaii, barely a minute after the earthquake, computers
at the Pacific Tsunami Warning Center spring into life as they pick
up the seismic signals. Any earthquake over magnitude 6 prompts
an automatic paging sequence to scientists on duty alerting them
in an instant.

Dr Stuart Weinstein
of the Pacific Tsunami Warning Center recalls “I noticed that
the trace of the seismogram was very full. It appeared as just kind
of one thick line going across the screen - and that told me that
it was a substantial earthquake”.

The warning
centre relies on data from a network of seismic stations to detect
earthquakes, but their system of coastal tide gauges and deep-ocean
pressure sensors triggered by tsunamis are located only in the Pacific.
Thanks to this system, the centre has successfully warned Pacific
coastlines against a series of killer waves for over 50 years –
and saved countless lives.

But –
in December 2004 - the Indian Ocean has no such system.

In the first
few minutes after the earthquake off Sumatra, data from seismic
stations has already alerted Weinstein and his colleague Dr Barry
Hirschorn to its location and size – enough to cause them
grave concern.

They send a
bulletin to alert Pacific coastlines of the earthquake, but with
no network of tsunami sensors in the Indian Ocean, Weinstein and
Hirschorn have no way of knowing if a tsunami has been triggered
there. Hirschorn later explains: “The seismic analysis can
only take you so far. We also looked into what water level might
be available, but because this was the wrong ocean the answer was
none”.

As they watch
events unfold, their frustration would turn to despair. When an
earthquake occurs under the ocean, its energy can dissipate as shockwaves
through the crust – or as tsunamis through the ocean. In this
case, just seconds after the earthquake, the energy it released
– the equivalent of 23,000 Hiroshima-sized atom bombs –
was instantly transferred to the water column above the ocean floor.
As the seafloor lifted, it displaced billions of tons of water above
it.

In Sumatra,
thousands begin their day, unaware of the approaching wave as it
charges towards them at over 600 mph. In the open ocean tsunamis
are virtually undetectable. Fishermen out here may not even notice
a tsunami passing underneath their boat. But as it nears land, it
rears up into a monster…

Simon Boxall
of the Southampton Institute of Oceanography explains: “as
the wave approaches the land the front of the wave slows down, to
four hundred, three hundred, two hundred miles an hour. The back
of the wave is still going at five hundred miles an hour, so the
back of the wave catches up with the front, and then you get this
big build-up of water.”

The amplified
wave can have a curious side-effect. Before it hits land, it draws
water from its leading edge, exposing the seabed for as much as
a mile. It’s a phenomenon that lures thousands to their deaths
as people rush down to pick up fish stranded on the exposed rocks.

Tsunamis rarely
roll towards land like a classic surfer’s wave. Instead they
surge forward like an onrushing flood. The leading edge builds into
a wall of water. They’re so deadly because the volume of water
behind them is so great.

Professor Bill
McGuire of University College, London, is an expert in the behaviour
of these lethal waves. He explains: “tsunamis have wavelengths
- the distance from the crest of one wave to the next wave - of
hundreds of kilometres. It will keep coming in maybe for five minutes
or more and it has enormous mass behind it.”

Just 15 minutes
after the earthquake, northern Sumatra is the first to experience
the full impact of the tsunami. Virtually no video footage is taken
of the wave that hits Sumatra. It is simply so big that anyone filming
it would have been killed.

The devastation
in the provincial capital, Banda Aceh, is unprecedented. Even those
used to disaster zones have never witnessed anything like it. And
residents living well inland are also dwarfed by the wave –
tragically, there’s nowhere to run.

Three-quarters
of all the tsunami’s victims die in Sumatra. But the great
wave is far from finished. Just 15 minutes later, the Andaman and
Nicobar islands are hit. Over 7000 die or go missing. Forty-five
minutes after the earthquake, scientists at the Pacific Tsunami
Warning Center are still unaware of the tsunami. But they are desperately
trying to analyse the earthquake data.

Another 15 minutes passes,
and the tsunami strikes Thailand. One hour has passed since the
earthquake. Cities are waking up and beaches are beginning to stir
into life. People everywhere have remained oblivious to the thousands
of deaths in Sumatra – and to the approaching tsunami, until
the sea rushes inland.

Fifteen minutes after
the tsunami first inundates the Thai coast, a deadlier second wave
strikes. Thousands are caught by surprise. According to Bill McGuire:
“in any particular earthquake you’ll get a different
tsunami train. In other words, there isn’t just one wave there
are usually several waves, and it doesn’t follow any particular
rule. Sometimes the first wave is the biggest one, sometimes there
are maybe two, three or even more relatively small waves and then
you get a huge one in the middle and then some smaller ones. But
normally you do get more than one wave, they are of different heights
and they arrive over different periods of time. It can be tens of
minutes, even hours, between the first wave and the last wave.”

It is 9.00am in Sri Lanka,
two hours since the birth of the waves. British holiday maker Shenth
Ravindra is crammed into a train with 1500 others. He is unaware
that he is about to be caught in the worst rail disaster in history.

The track follows a coastal
route, from Colombo to Galle – never far from the ocean. Ravindra
later recalls: “I heard the water and then all of a sudden
it came and started hitting the train, to such an extent that the
carriage got detached from the other carriages behind us and in
front of us. The water started to spill in, and I felt it come all
the way up to my chin. I thought ‘I’ve got to get out
of here’. I was able to climb through this doorway and make
my way onto the corner of the roof and the wall. And I was helping
put these children onto the train.”

No help is forthcoming
to the occupants of the train, nor to thousands of others along
the coast of Sri Lanka and India. And the survivors of the first
wave are completely unaware that a second, much bigger, tsunami
is minutes from impact.

According to Ravindra:
“When I saw the second wave coming, all I could see was a
wall of water that took up about 80 to 85 % of the horizon –
the sky was blocked. There were a lot of children surrounding me
and they were clinging onto me and hugging me and I was losing my
balance a little bit on the train. But luckily it just pushed the
carriage quite neatly along to the point where it wedged against
a house.”

Ravindra jumps from the
train onto the roof of the house. He is one of only a handful who
would survive. As the train disappears beneath the water, almost
everyone on board is drowned – almost 1500 people.

Throughout India and
Sri Lanka over 45,000 lives are lost. It is still only three-and-a-half
hours since the earthquake. At the Pacific Tsunami Warning Center,
the horror of the disaster is becoming apparent as an internet news
report confirms their worst fears. The earthquake they’ve
been monitoring has generated a massive tsunami.

Weinstein realises that
they have to warn Africa. “We then created a tsunami travel
time map for the Indian basin. It told us where the wave was presently,
and gave us an idea of how much time we had in order to warn people.
And then immediately we started to try to contact nations that were
ahead of the wave.”

Just under four hours
after the earthquake – and the Maldives are next on the tsunami’s
path of destruction. With the wave charging across the ocean at
600 mph, it seems like the Pacific Tsunami Warning Center is fighting
a losing battle. But Weinstein’s travel time map does prove
effective. Seven hours after the earthquake struck, the east coast
of Africa – on the far side of the Indian Ocean – is
next in line for the terror of the tsunami. Using data from the
travel time calculations, the scientists at the Pacific Tsunami
Warning Center are at last able to predict its path and raise the
alarm. In Kenya, this advance warning leads to the evacuation of
the shoreline – and there’s only one fatality.

Over the next 24 hours,
disturbances are detected throughout all the world’s oceans.
But the tsunami’s energy is dissipated as it progresses beyond
the Indian Ocean.

Its wake, however, will
resonate for years to come.

Richard Gross of NASA’s
Jet Propulsion Laboratory used seismic data to make some startling
calculations on the results of the record earthquake: “it
has caused the mass of the plates to be out of balance, which has
in turn caused the Earth to wobble by about two-and-a-half centimetres.
This is just like the tyre on your automobile. If the tyre is not
balanced it will not spin smoothly.”

Not only did the earthquake
push the planet off balance, it also shortened the length of the
day by about 3 millionths of second!

For most people, the
tsunami was totally unexpected, even though they are all too common
in southeast Asia. Last December there was no warning system in
the Indian Ocean. Now, sensors for a tsunami network are being installed
around Indonesia.

Despite the promise of
this early warning system, there are still many thousands of people
living near the sea in Banda Aceh. They remain exposed to danger,
there’s no way to provide an alert quickly enough if another
earthquake occurs so nearby. The only possible way they can be protected
is to either move much further inland or to build a large protection
sea wall as they do in Japan.

Protection against tsunamis
however remains a matter of cost and politics, even though these
destructive waves are a global hazard. Tsunamis pose a direct threat
to 80 percent of the world’s population. And it’s not
a case of ‘if’ but ‘when’.

December 2004 was a stark
reminder of the precariousness of our co-existence with Nature.
In reality, with only 15 minutes to warn and evacuate northern Sumatra,
even the most sophisticated warning system may not have been enough
to save many of the people who died there.

But it would have saved
many of the thousands who died in eleven other countries…

More information:

- maps, animations
and more from America’s National
Oceanic and Atmospheric Administration